Effect of mononuclear cell factors on calcium transport in sarcoplasmic reticulum vesicles

The effect of supernatants from cultures of mitogen-stimulated human mononuclear cells on calcium transport by sarcoplasmic reticulum was examined. Calcium transport was assayed by measuring the time course of calcium accumulation by sarcoplasmic reticulum incubated with supernatants from stimulated mononuclear cells was 20% less than that by vesicles exposed to control supernatants (P less than 0.001). In contrast, no difference in calcium-dependent ATPase activity was noted between vesicles incubated with either active or control supernatants. The results suggest that mononuclear cell factors disturb calcium transport in sarcoplasmic reticulum membrane.